1. Field of the Invention
The present invention relates generally to a cabinet for a machine cooled by ventilation, the cabinet containing an air filter held in contact with a filter-presence detection device so that the machine is stopped if the air filter is removed. More particularly, the invention concerns cabinets enclosing machines with high thermal dissipation, such as computers used in medium and large size information processing systems.
2. Discussion of the Prior Art
A machine air filter is ordinarily made of a grid supported by a frame. The air filter is generally inserted into the machine cabinet by sliding on guides at the base of the cabinet parallel to the floor. The air filter is designed to stop dust and foreign objects that could be aspirated by the fans and then circulated within the machine. The dust and objects may interfere with the normal functioning of the machine and may in fact damage the machine. In a computing system especially, the accumulation of dust on the electrical components and their interconnection elements changes the desired quality of cooling and of the electrical insulation. The presence of the filter is important and it is thus monitored continuously by a detector, usually a switch actuated by the fastening edge of the filter when the filter is correctly installed in the machine.
Using air filters poses a maintenance problem. Normally, the filter will have to be changed periodically. To determine when the filter needs to be changed, the vacuum created by the fans is monitored. When a signal corresponding to the vacuum drops below a critical threshold, indicating that the air flow has dropped below the minimum airflow needed for proper operation of the machine, a signal is generated signaling that the air filter needs changing. However, since removal of the filter activates the presence detector which in turn stops the machine, it is generally best to stop the machine in a controlled manner in order to change the filter. Stopping and restarting a computer and returning it to its normal operating state are in fact operations that are very troublesome and expensive if the computers are turned off simply to change a filter. In practice therefore, the filter is thus changed sooner or later than it should be. While the machine is stopped, a part of the dust set into vibration at the time the filter is removed, due to the mechanical removal of the filter, is attracted by electrostatic effects towards the electrical components in the computer and their supports. The dust may, in the long run, adversely affect cooling or the electrical insulation. Another significant portion of the dust falls onto the floor. This dust is aspirated when the machine is started up again and partially fouls the new filter. Another drawback of the prior art filters and machine cabinets is that maintenance cannot be done without stopping the machine. This considerably aggravate the problem of replacing the filter.
Certain conditions of the machine usage create other problems. For example, there are certain countries which have regulations requiring that a metal plate be placed permanently under components that are easily inflammable or apt to emit noxious fumes when there is a fire. The remedy used actually consists of placing a metallic plate that is massive, cumbersome, and unaesthetic below the machine. Furthermore, it is difficult to put the metallic plate in place. It is necessary to place the machine at the desired location and to mount it on jacks in order to position it in the proper relationship to the floor and the plate.
The present invention solves these prior art problems with a simple, efficient, and inexpensive apparatus.